The present invention relates to a body fluid measuring apparatus for measuring the concentration of a specific component contained in body fluid such as glucose contained in blood, and to a body fluid sampler for the apparatus.
For diabetes treatment, it is necessary to maintain, in a normal range, the concentration of glucose (hereinafter xe2x80x9cblood glucose levelxe2x80x9d) contained in the blood of a diabetes patient. An important treatment is the blood glucose level management by the patient. Particularly for treatment of insulin-dependent diabetes, the patient should inject insulin to keep the blood glucose level in a normal range. Therefore, measurement of the blood glucose level is essential for the patient.
A portable apparatus usable by a diabetes patient by himself or herself for measuring the blood glucose level is commercially available. For example, JP-B-8-20412 discloses such a blood glucose level measuring apparatus. The blood glucose level measuring apparatus comprises a main unit and a disposable test piece to be mounted on the main unit. An enzyme electrode is formed on the test piece. With this measuring apparatus, when the tip of the test piece contacts blood, a portion of the blood is sucked in by a reacting portion of the test piece by capillary phenomenon to cause an enzyme reaction and an electrochemical reaction in the reacting portion. As a result, an anode current flows to the electrode of the test piece. The anode current is converted to a blood glucose level in an arithmetic circuit in the main unit of the apparatus, and the result is represented on a display.
In order to bring an analyte such as blood into contact with a test piece in the measuring apparatus, a tool named xe2x80x9clancetxe2x80x9d is commonly used, as disclosed in JPA-9-266898 for example. The lancet is a tool used for making a small hole or cut in the skin of a finger tip, for example, of a patient. Upon bleeding from the hole or cut, blood is brought into contact with a predetermined site of the test piece for further supply of blood used for measurement of the blood glucose level.
However, with the conventional common self-measurement of the blood glucose level, the lancet for sampling blood is separate from the measuring apparatus, so that the two tools need to be carried by the patient. Moreover, it is necessary to separately perform the steps of injuring the skin with the lancet and of bringing the bleeding blood into contact with the test piece, thus making measurement still complex. In particular, when bringing the blood into contact with the test piece, since a predetermined amount of blood needs to be brought into contact with a predetermined portion of the test piece, it is difficult for an untrained or weak-sighted patient to perform this step quickly and properly.
In addition, the above-described conventional blood glucose level measuring apparatus is designed to suck blood from a hole at the tip of the test piece onto a planar enzyme electrode in the reacting portion by capillary phenomenon. Therefore, at least 3 to 5 xcexcl of blood needs to be brought into contact with the test piece to ensure that a necessary amount of blood reaches the reacting portion. If the amount of blood is insufficient or if a sufficient amount of blood is not deposited appropriately on a small area surrounding the tip hole of the test piece, the apparatus may suffer erroneous measurements. In particular, such a case is more likely to occur with respect to patients such as infants and the elderly who tend to suffer insufficient bleeding of blood from a cut.
JP-A-9-94231, JP-2616331, and JP-A-9-89885 disclose a measuring apparatus which comprises a lancet and an enzyme electrode for providing the dual functions of blood extraction and measurement.
However, use of the apparatus of JP-A-9-94231 requires the sucking of blood by piercing the skin with a needle-like lancet during blood glucose level measurement, which causes continual pain. Further, since disposability of the blood sampling unit is not intended, problems therefore arise with regard to hygienic management and utility for repeated use. The apparatus of JP-2616331 also necessitates the sucking of blood with a needle-like lancet held stabbed into the skin and disposability of the blood sampling unit is not intended. On the other band, the apparatus of JP-A-9-8985 is designed to instantaneously complete a skin injuring operation with a lancet However, this apparatus is equipped with two pairs of electrodes in addition to the lancet and thereby a process for manufacturing the apparatus becomes complex with a resultant increase of the manufacturing cost. Moreover, with this apparatus, no ideas have been put forward concerning alleviation of pain in blood sampling by reducing the amount of blood for measurement.
An object of the present invention is to eliminate or relieve the above described problems. Specifically, the object of the present invention is to simplify the patient""s action needed for measurement. A further object of the present invention is to provide a body fluid measuring apparatus and a body fluid sampler therefor, which require a significantly decreased amount of analyte for measurement with a high reliability to thereby relieve the pain attendant therewith.
According to a first aspect of the present invention, there is provided a body fluid measuring apparatus comprising a main body and a body fluid sampler fitted to the main body. The body fluid sampler comprises a fixed member fixed to the main body and a movable member guided by the fixed member. The fixed member is formed with a body fluid-sucking chamber open at a tip of the fixed member and a through-hole communicating therewith. The movable member comprises a lancet acting as a first electrode and is reciprocatively movable for bringing the tip of the lancet into and out of the tip of the fixed member. The body fluid-sucking chamber is provided with a second electrode and a reactive layer containing a reactive reagent necessary for measurement. The main body comprises an electronic circuit for providing a measurement on the basis of an electrical signal from the lancet as the first electrode and a second electrode, and a drive mechanism for driving the movable member for causing the tip of the lancet to project from the tip of the fixed member.
Preferably, the fixed member comprises a cylindrical electrode acting as the second electrode and an insulator for electrically separating the cylindrical electrode from the lancet. The cylindrical electrode and the lancet are concentrically arranged.
Preferably, a surface of the insulator facing the lancet is hydrophobically treated.
Preferably, the reactive layer is provided over an entire wall surface defining the fluid-sucking chamber in the cylindrical electrode.
Preferably, the drive mechanism comprises an automatic drive mechanism for driving the movable member to first cause the tip of the lancet to project from the tip of the fixed member and to subsequently cause the tip of the lancet to retreat from the tip of the fixed member.
Preferably, the main body has a fixed terminal connected to the electronic circuit, and the movable member of the body fluid sampler comprises a contact portion in slidable contact with the fixed terminal for electrically connecting the lancet to the fixed terminal.
Preferably, the main body has an annular spring terminal for electrically connecting the second electrode to the electronic circuit, and the fixed member of the body fluid sampler is detachably fixed to the main body under urging of the annular spring terminal.
Preferably, the fixed member is provided with an air-vent hole for enabling the fluid-sucking chamber to communicate with an external space.
Preferably, the inner diameter of the cylindrical electrode is 0.4-1.2 mm, and more preferably 0.5-0.8 mm.
Preferably, the tip of the lancet is pointed like a needle, and the outer diameter thereof is 0.2-0.4 mm.
Preferably, each of the first electrode and the second electrode is formed from carbon, a noble metal, or a composite of these materials.
In use of the body fluid measuring apparatus according to the first aspect of the present invention, the tip of the body fluid sampler mounted to the apparatus, i.e. the tip of the fixed member,is pressed against a finger tip, for example, of a patient, the movable member is driven forward by operation of the drive mechanism of the main body to injure the skin of the patient finger tip with the lancet tip of the movable member projecting beyond the tip of the fixed member. Preferably, the movable member is subsequently moved backward for a predetermined distance, but the lancet tip still remains in the fluid-sucking chamber even in this retreated state. While holding the tip of the fixed member pressed against the finger tip for some time, blood bleeding from the injury is sucked into the fluid-sucking chamber by the capillary phenomenon. The sucked blood dissolves the reactive layer provided in the fluid-sucking chamber and contacts the electrode (operative electrode for example) mounted on the fixed member in exposure to the fluid-sucking chamber as well as the lancet as the electrode (counterpart electrode, for example). The reactive layer contains, for blood glucose level measurement, a reactive reagent such as glucose oxidase which is an oxidization enzyme, and potassium ferricyanide as a mediator.
When the reactive layer is dissolved in blood, an enzyme reaction starts, as represented by the following formula (1) As a result, potassium ferricyanide contained in the reactive layer is reduced to cumulatively produce potassium ferrocyanide which is a reduced-type electron carrier. The amount of potassium ferrocyanide is proportional to the concentration of the substrate, i.e., the glucose level of the blood. The reduced-type electron carrier produced in a predetermined time is electrochemically oxidized as represented by the following formula (2), thereby generating an anode current. The electronic circuit in the main body of the measuring apparatus performs calculation to determine the glucose level (blood glucose level) based on the detected anode current. Preferably, the result of measurement is displayed on a display mounted on a surface of the main body. 
In this way, with the body fluid measuring apparatus according to the first aspect, it is possible to perform body fluid measurement such as blood glucose level measurement easily and properly only by causing the lancet to project from the tip of the fixed member while keeping the tip of the body fluid sampler in the main body pressed against the finger tip of the patient. The process required for using the body fluid measuring apparatus according to the present invention is much simpler than the conventional measuring process which requires the steps of injuring the skin with a lancet and bringing the bleeding blood into contact with a test piece on a measuring apparatus.
Moreover, in the case of an electrode structure wherein the electrode of the fixed body is cylindrical to accommodate therein the lancet as a counterpart electrode, the amount of body fluid necessary for measurement can be reduced. For example, assuming that the cylindrical electrode has an inner diameter of 0.6 mm and the fluid-sucking chamber has an axial length of 1 mm, the electrode area is 1.884 mm2 and the fluid-sucking chamber has a volume of 0.2826 xcexcl. Due to the lancet having a portion residing in the fluid-sucking chamber, the required volume of the analyte further decreases. In addition, the bleeding blood directly entering the fluid-sucking chamber from the skin need only flow a very short distance before reaching the two electrodes. This means that the amount of analyte required by the body fluid measuring apparatus according to the present invention is smaller than the volume corresponding to the fluid-sucking chamber. Considering that the conventional measuring apparatus mentioned in the BACKGROUND ART portion requires 3-5 xcexcl of analyte, it can be understood how small the amount of analyte required by the electrode structure according to the present invention is. The smaller the required amount of sample is, the higher is the reliability of measurement and the lower is the pain.
According to a second aspect of the present invention, another body fluid measuring apparatus is provided which comprises a main body and a body fluid sampler fitted to the main body. The body fluid sampler comprises a fixed member fixed to the main body and a movable member guided by the fixed member. The fixed member is formed with a through-hole. The movable member comprises a lancet and is reciprocatively movable for bringing the tip of the lancet into and out of the tip of the fixed member. The lancet comprises a tube, an axial core inserted therein, and an insulator for electrically separating the tube and the core. The tube serves as a first electrode, whereas the axial core serves as a second electrode. The tip of the lancet is provided with a reactive reagent for measurement. The main body comprises an electronic circuit for providing a measurement on the basis of an electrical signal from the tube and the axial core, and a drive mechanism which drives the movable member for causing the tip of the lancet to project from the tip of the fixed member.
Preferably, the tube projects further tipwise than the axial core and the insulator, and the reactive reagent is attached to the tip of the axial core.
Preferably, the drive mechanism comprises an automatic drive mechanism for driving the movable member to first cause the tip of the lancet to project from the tip of the fixed member and to subsequently cause the tip of the lancet to retreat from the tip of the fixed member.
Preferably, the main body has a first and a second fixed terminals connected to the electronic circuit. Further, the movable member comprises a first contact portion in slidable contact with the first fixed terminal for electrically connecting the tube to the first fixed terminal and a second contact portion in slidable contact with the second fixed terminal for electrically connecting the axial core to the second fixed terminal.
Preferably, the fixed member is provided with an air-vent hole for enabling fluid-sucking chamber to communicate with an external space.
The body fluid measuring apparatus according to the second aspect of the present invention functions mechanically, chemically, and electrically in substantially the same way as the apparatus according to the first aspect. Blood bleeding from the injury is sucked by the tip of the lancet by the capillary phenomenon. While dissolving the reactive reagent attached to the tip of the axial core, the sucked blood contacts the axial core of the lancet (operative electrode for example) as one electrode and the tube of the lancet as the other electrode (counterpart electrode for example.) Thereafter, the anode current is measured by the electronic circuit inside the main body.
As in the preferred embodiment, if the tube of the lancet projects further tipwise than the axial core and the insulator to form a very small space at the tip of the lancet with the reactive reagent attached to the tip of the axial core, blood entering the small space reliably contacts both the axial core and the tube as electrodes. As a result, a very small amount of blood gives rise to a current sufficient for measurement.
Consequently, the body fluid measuring apparatus according to the second aspect provides the same advantages as that according to the first aspect. Furthermore, the blood amount to be sampled may be an amount needed only for contact with the two kinds of electrodes formed at the tip of a very thin lancet and thus, the tip of the lancet need only pierce the skin to a smaller depth than is necessary for the apparatus according to the first aspect. This contributes to additional relief of the pain while also improving reliability of measurement.
A third aspect of the present invention provides a body fluid sampler mounted, in use, on a body fluid measuring apparatus. The body fluid sampler comprises a fixed member and a movable member guided by the fixed member. The fixed member is formed with a body fluid-sucking chamber open at a tip of the fixed member and a through-hole communicating therewith. The movable member comprises a lancet acting as a first electrode and is reciprocatively movable for bringing the tip of the lancet into and out of the tip of the fixed member. The body fluid-sucking chamber is provided with a second electrode and a reactive layer containing a reactive reagent necessary for measurement.
Preferably, the movable member comprises a contact portion for slidable contact with a fixed terminal mounted to a main body of the body fluid measuring apparatus to which the body fluid sampler is attached, and the contact portion is held in conduction with the lancet.
The body fluid sampler according to the third aspect of the present invention is used as one for the apparatus according to the first aspect. Therefore, the body fluid sampler according to the third aspect of the present invention has the same advantages as those described concerning the first aspect.
According to the fourth aspect of the present invention, another body fluid sampler is provided which is mounted, in use, on a body fluid measuring apparatus. The body fluid sampler comprises a fixed member and a movable member guided by the fixed member. The fixed member is formed with a through-hole. The movable member comprises a lancet and is reciprocatively movable for bringing the tip of the lancet into and out of the tip of the fixed member. The lancet comprises a tube, an axial core inserted therein, and an insulator for electrically separating the tube and the core. The tube serves as a first electrode, whereas the axial core serves as a second electrode. The tip of the lancet is provided with a reactive reagent for measurement.
Preferably, the movable member comprises a first contact portion for slidable contact with a first fixed terminal mounted to a main body of the body fluid measuring apparatus to which the body fluid sampler is attached, and the first contact portion is held in conduction with the tube. The movable member also comprises a second contact portion for slidable contact with a second fixed terminal mounted to the main body, and the second contact portion is held in conduction with the axial core.
The body fluid sampler according to the fourth aspect of the present invention is used as one for the apparatus according to the second aspect. Therefore, the body fluid sampler according to the fourth aspect of the present invention has the same advantages as those described concerning the second aspect.
Other features and advantages of the present invention will become clear from the detailed description presented below with reference to the drawings.